98 NEW YORK STATE MUSEUM 
Let us see now how the other paleontologic and zoologic evidence 
agrees with this hypothesis. We saw already that in Protobalanus 
we have a connecting link in which the 5 lateralia of each side have 
become uniform in shape. ‘This leads to the recent Catophragmus 
with 3 subequal lateralia on each side, which in the common Balanus 
have become further reduced (by coalescence!) to 2. 
Equally convincing is the ontogenetic evidence in recent forms. 
Since Darwin's fundamental investigation of the barnacles, the 
Balanidae are currently regarded as derived from the Lepadidae 
through reduction of the peduncle. The whole order of Cirripedia 
or barnacles, on account of their ontogeny and especially the bivalved 
“‘ Cypris-stage ’ through which the larval form passes after the 
Nauplius-stage, are commonly derived from the ostracods, while 
Balfour (1880, p. 424), emphasizing both the large bivalve shell and 
the compound eyes, has urged “the independent derivation of the 
Cirripedia from some early bivalve Phyllopod-form.” 
This view is adopted by Korschelt and Heider in their authorita- 
tive “ Text-book of the Embryology of Invertebrates” (1899, 
p. 209). They state: “ We must, however, in consequence of the 
presence of the so-called Cypris-stage (with a bivalve shell) which 
occurs in their metamorphosis and brings about the transition from 
the free to the attached life, assume for them a similarly attached 
ancestral form, which we must seek among the Phyllopoda.” 
It seems further significant to us that the free-swimming Cypris- 
stage, which appears after a series of Nauplius-stages, is followed 
by the attached Cypris-stage (pupa), from which proceeds the adult 
stage (ibid. p. 209). So also in the ontogeny, as well as in the prob- 
able phylogeny, it is thus the bivalved stage, which becomes attached 
and thus marks the turning point in the individual and racial 
development. 
It is this latter view that is well borne out by the interpretation 
we put on our material; or by tracing the acorn barnacles back to 
Rhinocaris-like phyllocarids with 4 plates. For while the Phyl- 
locarida Packard (leptostraca Claus), at present represented only 
by the well-known relict Nebalia geoffroyi, of the Gulf of Trieste, 
were formerly a part of the Phyllopoda, and have been removed to 
the Malacostraca on account of their more advanced structure, they 
still retain in their phyllopodiform legs and other characters the evi- 
dence of their derivation from the more primitive Phyllopoda s. sr. 
and are properly considered as connecting the Malacostraca with the 
less advanced Entomostraca, especially the phyllopods. 
